Experience Dictates By the Post-war Chassis Sgt. E. G. Frogley
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A R.E.M.E. Sergeant Gives His Views on Many Inttmate Matters Relative to the Design of Post-war Chassis. The Transmission Responsible for Most Breakdowns •
THE article in your issue dated July 21, entitled " Some Pointers for Post-war Designs," made .very interesting reading. As a vehicle engineer having many and varied types of machine through my •department every day (oh! for standardization), I can appreciate all the points raised. In the first place, I definitely am all for fixed starting handles. I wonder how many have been lost, and how many crankshaft dogs have been chewed up beyond repair by misuse of this illdesigned accessory? But this is only a minor point. What about oil seals?
We are having much trouble, lately, with this necessary evil. It seems that synthetic rubber is being used as a sealing agent, whereas I should imagine that leather would be much more satisfactory and economical, especially in war-time. Believe me, it is no light job stripping down some of these delightfully complicated transmission systems to fit one oil seal. The trouble is when one machine of a certain series comes in, we can be assured that it will, sooner or later, be followed by all its clan. We've had some!
Lack of Accessibility And accessibility! I can quote a certain American recovery vehicle, in which it is necessary to remove the cab even to see the engine, let alone work on it.
• For that matter, some of our own machines leave much room for improvement. On several of them, the cab has to be removed before the engine assembly can be lifted out. Of course, 'this is all very well in a service station, but imagine doing this sort of thing under the conditions which often obtain over here in Italy.
From the servicing point of view, overhead valves are favoured, as, in many cases, it has been impossible to get to the vehicle with the necessary reseating equipment, and when the complete head and valves can be taken to the bench much time is saved. But, then, we don't .get half the valve trouble with engines of the side-valve type as compared with o.h.v. types. so which is the less of the two evils? And dealing with carburetters, I am convinced. that the modern down-draught instruinent is responsible for the excessive cylinder wear which we are experiencing just now.
It would be interesting to compare the lives of two identical units, say Bedfords, using the two types of carburetter and induction systems; the oil should he checked for dilution after a week's running. Ignition systems are, I think, as nearly perfect as we shall get them, apart, in some cases, from inaccessibility. Of course, dual ignition 'would be a good thing, but would add to the expense and maintenance. In any case, I think the battery is still the most ill-treated component in the majority of machines, and, in cense
quence, the prime cause of nearly all ignition failures. This, again, is a case, usually, of inaccessibility, and it is, as often as not, forgotten until it starts giving trouble. I think the worst possible place for a battery is under the floorboards of the cab, which is constantly in a filthy condition.
One point worthy of attention is the distributor shaft bearing in the distributor body. Where there is any play present, due to wear, it is impossible to maintain the specified breaker gap. Surely, an adjustable bearing could be fitted; it wouldn't be expensive, and a marked difference in operation would result.
The point your correspondent raises regarding the shearing of fan blades is easily remedied. This always occurs in cases where the blades are riveted to the hub or fan centre': A one-piece stamping never gives this trouble, and is, I skould imagine, pasier to make. If we are to have four-wheel-drive machines, is it beyond the realms of possibility that one day we may have a differential that may be locked by a control in the driver's cabin? In many cases these machines are almost useless, as wheelspin, with resultant crabbing, is unavoidable, I believe there is a vehicle fitted with a device of this kind, but I have yet to see it in action.
It would be interesting to know just how much horse-power is wasted when a four-wheel-drive machine is operating on the road in normal drive. For example, in North Africa we used a mountain road for a. test route (for the benefit of readers who may know the country—the road from Ghardimaou to Souk Ants). On one hill, a Standard 27 h.p. three-tonner of the normal-drive type used to romp up in top gear, whilst the four-wheel-drive
• version of the same machine, with almost identical engine, required second gear for the same ascent.
In my opinion, these machines are much under-powered, and are too prone to transmission troubles to be of any practical use to us at the cessation of hostilities.
We have had little, gearbox trouble; it is always in the final drive. Halfshaft fractures are rare, and I do not think that, as your correspondent suggests, flexible shafts are necessary. Preferably: standardize the " L'ayrub " type • of propeller shaft coupling, anil I think that our tzturstnission ailments will very much lessen. Clutches have caused us but little bother, apart from thOse Which have been maltreated; there has been occasional shearing of
the rivets securing the splined centre to the disc.
Perhaps it won't be too much to expect to see the _hydraulic type of transmission in more general use before many more years have passed. Manufacture should present little or no difficulty, and its cost should be far less than the modern conventional type of friction clutch. I have seen an American version_ of this form of drive fabricated from steel pressings, and it is nearly 100-per cent. efficient.
By far the greatest cause of vehicle casualties is transmission failure. Next comes the engine, due to valve trouble. undoubtedly caused by leaded fuel.
Electrical breakdowns are almost non-existent, and, apart from minor defects, do. not necessitate any vehicle being off the road for more than an hour or so. Chassis, except sometimes in the case of the cheaper types of vehicle, cause very. little trouble with normal use, even on these super-potholed roads in Italy. However, on one well-known British threetonner we have had to modify the frame by reinforcing between the engine and cab for, a distance of 3 ft. Before this was done many casualties were caused by the chassis fracturing just behind the rear front-spring hanger.
In some cases, springs leave a lot to be desired; we still have quite a number of main-leaf breakages every week, mostly due to the abnormal road surfaces. Centre bolts still give trouble, but this, more often than not, is the fault of the driver 'failing to tighten the tj-bolts at frequent intervals.
I think the ideal post-war road transport vehicle may be summarized by the following specification
Engine—Preferably CI., but if it has to be petrol, let it incorporate the following features:—(1) Accessibility of coMponents, (2) sodium-cooled exhaust valves, (3) hydraulic tappets (selfadjusting), (9) splash lubrication as well as pressure lubrication to big-end bearings, (5) easily removable wet cylinder liners (a. la Italian 0.M.), (6) in the case of six-cylinder engines seven main bearings, (7) normal up-draughttype of carburetter, (8) a first-class fool-proof engine-speed governor.
Transmission.—Fluid Flywheel with positive seal at output shaft; five-speed, close-ratio gearbox no synchromesh, please; with five speeds, no booster or overdrive will be necessary; universal couplings of the Layrub type; worm drive, and fully floating axle shafts.
Brakes.–Meehanical servo (-similar to the Rolls-Royce system) coupled to Girling-type shoes.